The present invention relates to an element for converting electric energy into mechanical energy to be used, for example, for actuators, various vibrators, displays, and relays, or a capacitor element to be used, for example, for filters and resonance circuits. In particular, the present invention relates to a ceramic element based on the use of the phase transition between the anti-ferroelectric phase and the ferroelectric phase, a display device based on the ceramic element to be used for driving a picture element (image pixel) to perform display, a relay device based on the ceramic element to be used for driving a relay to perform switching, and a capacitor based on the ceramic element to be used for varying the capacitance.
Recently, it has been demanded, for example, in the fields of optics and precision manufacturing, to use a displacement element for adjusting the optical path length or the position on the order of submicron.
In order to respond to such a demand, development is being advanced for actuators which utilize occurrence of displacement based on the inverse piezoelectric effect caused when an electric field is applied to a piezoelectric material such as a ferroelectric substance.
In such a trend, the present applicant has also previously proposed piezoelectric/electrostrictive film-type elements made of ceramics, which can be preferably used for various applications, as described, for example, in Japanese Laid-Open Patent Publication Nos. 3-128681 and 5-49270.
The previously proposed piezoelectric/electrostrictive film-type element has such excellent features that it serves as a compact and inexpensive electromechanical conversion element with high reliability to provide a large displacement at a low driving voltage, in which the response speed is quick, and the generated force is large. The piezoelectric/electrostrictive film-type element is useful to be used, for example, as a constituting component of actuators, displays, and relays.
The piezoelectric/electrostrictive film-type element described above is operated such that the mechanical displacement is obtained in accordance with the inverse piezoelectric effect or the electrostrictive effect by applying a voltage to the piezoelectric/electrostrictive operating section (actuator element). Therefore, the piezoelectric/electrostrictive film-type element is advantageous in that the magnitude of the displacement amount can be precisely controlled with respect to the applied voltage, while it is disadvantageous in that it is difficult to obtain a large displacement-generating force when a minute element is used.
In the case of the piezoelectric/electrostrictive film-type element, when it is required to maintain a state of displacement in one direction for a certain period of time, it is necessary to continuously apply the voltage to the piezoelectric/electrostrictive film operating section.
For this reason, for example, when the piezoelectric/electrostrictive film-type element is applied to a display device as disclosed by the present inventors in Japanese Laid-Open Patent Publication No. 7-287176, it is necessary to continuously apply the voltage to the piezoelectric/electrostrictive film operating section throughout the period in which the light emission state should be maintained.
In this case, for example, when a display device, which comprises a large number of light-emitting elements disposed two-dimensionally, is produced, it is necessary to arrange electric wiring for driving each of the elements one by one. Such an arrangement involves large restriction in view of design and production.
The present invention has been made considering the problems as described above, an object of which is to provide a ceramic element which makes it possible to precisely control the magnitude of displacement amount with respect to an applied voltage, and obtain a large displacement-generating force exceeding those obtained by the piezoelectric/electrostrictive film-type element even when a minute element is used.
Another object of the present invention is to provide a ceramic element which makes it possible to maintain a displacement amount approximately equivalent to that obtained when a driving voltage is applied, in the no voltage-loaded state or in a low voltage-loaded state after completion of application of the driving voltage, in addition to the condition described above.
Still another object of the present invention is to provide a ceramic element which makes it possible to simplify electric wiring for driving the element and effectively reduce the production cost when a variety of applications (for example, display devices and filters) are constructed, in addition to the condition described above.
Still another object of the present invention is to provide a display device which consumes less electric power and which makes it possible to simplify electric wiring for driving the display device and effectively reduce the production cost and the running cost.
Still another object of the present invention is to provide a relay device which consumes less electric power and which makes it possible to simplify electric wiring for driving the relay device, effectively reduce the production cost and the running cost, and realize various types of switching operations.
Still another object of the present invention is to provide a capacitor which makes it possible to easily construct a thin-type capacitance-variable capacitor with its capacitance changeable in an analog manner, and facilitate miniaturization of, for example, parametric amplifiers incorporated with the variable capacitor, automatic frequency control circuits (AFC), and various types of communication instruments.
According to the present invention, there is provided a ceramic element comprising an operating section having an anti-ferroelectric film and at least a pair of electrodes formed on the anti-ferroelectric film, a vibrating section for supporting the operating section, and a fixed section for supporting the vibrating section in a vibrating manner.
The principle of operation of the anti-ferroelectric film will now be explained. When the ferroelectric phase is induced in the anti-ferroelectric film in accordance with the change in, for example, the temperature, the stress, and the electric field, then the strain xF is given by the following expression:
xF=Q(1+xcexa9)PF2
wherein PF represents the ferroelectric polarization, and it satisfies PF=(Pa+Pb)/2, and wherein Pa and Pb represent the sub-lattice polarization.
In the case of the perovskite type crystal, the electrostrictive constant Qh (=Q11+2Q12) has a positive value. Therefore, the spontaneous volume strain of an ordinary ferroelectric is always positive, while in the case of the anti-ferroelectric, its spontaneous strain xA may be positive or negative depending on the value of xcexa9. In the case of lead zirconate (PbZrO3), there is given xcexa9=1.8.
It is assumed that the absolute values |Pa|, |Pb| of the sub-lattice polarization are not changed so much before and after the anti-ferroelectric phase-ferroelectric phase transition. On this assumption, the amount of strain change xcex94x involved in the transition is represented as follows:
xcex94x=xFxe2x88x92xA=2Qxcexa9PF2
Further, it is known that large displacement is obtained when the anti-ferroelectric phase-ferroelectric phase transition is utilized, rather than when the paraelectric phase-anti-ferroelectric phase transition is used.
It is known, for example, that a ceramic (polycrystal) derived from lead zirconate titanate (PZT) successively causes transition to the pseudo-tetragonal anti-ferroelectric phase and the orthorhombic ferroelectric phase in accordance with the decrease in temperature from the cubic paraelectric phase which is the phase at a high temperature. Therefore, when a composition, in which the anti-ferroelectric phase is stable at room temperature, is selected, it is possible to easily induce the ferroelectric phase by applying an external electric field. It is expected that a large change in strain takes place in accordance therewith.
Once the ferroelectric phase is induced, it is not returned to the anti-ferroelectric phase even when the electric field is made to be zero, exhibiting the xe2x80x9ceffect to store the strain state of the ferroelectric phase (shape memory effect)xe2x80x9d. In order to make restoration to the original anti-ferroelectric state, a small reverse bias voltage may be applied, or temperature-programmed annealing may be performed.
That is, the anti-ferroelectric causes the electric field-induced phase transition by applying the external magnetic field. Therefore, the phase transition occurs from the anti-ferroelectric phase to the ferroelectric phase to cause the volume change by applying, to the pair of electrodes, a voltage not less than a predetermined voltage. Thus, it is possible to easily obtain the mechanical displacement.
Since the displacement amount is brought about by the phase transition, it is impossible, unlike the piezoelectric/electrostrictive element, to accurately control the magnitude of the displacement amount by selecting the value of the voltage to be applied. However, on the contrary, the ceramic element exhibits a characteristic that the displacement can be continuously maintained even when the applied voltage is lowered provided that the applied voltage is not lowered up to a predetermined voltage at which the phase transition occurs from the ferroelectric phase to the original anti-ferroelectric phase.
Based on this knowledge, when the ceramic element according to the present invention is considered, the ceramic element has the structure in which the operating section having the anti-ferroelectric film is formed on the vibrating section which is vibratingly supported by the fixed section. Accordingly, when the predetermined voltage is applied to the pair of electrodes, the anti-ferroelectric film of the operating section undergoes the electric field-induced phase transition caused by the external electric field brought about by the predetermined voltage. The mechanical displacement is generated in accordance with the phase transition. The displacement is amplified by the vibrating section, and the operating section is displaced in a first direction (for example, in a direction for the operating section to face the free space).
Once the operating section is displaced in the first direction, the displacement is maintained as it is even when the voltage application to the pair of electrodes is stopped (for example, when the electric field is made to be zero). Accordingly, it is unnecessary to continuously apply the voltage to the pair of electrodes even when the displacement generated in the operating section is required to be maintained for a certain period of time. In order to restore the displacement generated in the operating section to the original state, a small reverse bias voltage, specifically a voltage to cause the phase transition from the ferroelectric phase to the anti-ferroelectric phase may be applied to the pair of electrodes.
As described above, in the ceramic element according to the present invention, the amount of mechanical displacement is changed in a digital manner depending on the voltage applied to the pair of electrodes. Further, the displacement amount, which is equivalent to that obtained upon the voltage application, can be maintained in the no voltage-loaded state after completion of application of the voltage.
It is preferable for the ceramic element constructed as described above that the pair of electrodes have a form in which an intensity of an electric field, which is generated by applying a voltage to the pair of electrodes, spatially differs. Accordingly, the following phenomenon occurs. That is, for example, a part of the region of the operating section is displaced by applying a low voltage, and the other region is not displaced. After that, for example, a high voltage is applied to the pair of electrodes, then the other region also undergoes displacement, and the entire operating section makes displacement.
In other words, the operating section successively makes displacement in a digital manner, starting from the portion to which a relatively high electric field is consecutively applied in accordance with the increase in the applied voltage.
As described above, in the ceramic element according to the present invention, a plurality of displacement forms and/or displacement distributions can be selected depending on the value of the voltage applied to the pair of electrodes. Thus, it is possible to realize semi-analog or quasi-analog mechanical displacement.
Specifically, in order to obtain the element which is excellent in selectivity, for example, for the displacement form, the ceramic element may have a region in which a distance between the pair of electrodes is large and a region in which the distance between the pair of electrodes is small. The region in which the distance between the electrodes is large and the region in which the distance between the electrodes is small are formed by using a pattern of the pair of electrodes. Accordingly, when a constant voltage is applied to the pair of electrodes, a high electric field is always generated in the small-distance region than in the large-distance region. Therefore, when the applied voltage is low, only the portion of the anti-ferroelectric film corresponding to the small-distance region is subjected to the phase transition at a certain voltage to cause displacement. Subsequently, when a larger voltage is applied to the pair of electrodes the large-distance region is subjected to the phase transition at a certain voltage to cause displacement. As a result, the following effect can be obtained. That is, two displacement forms or displacement distributions can be arbitrarily selected by selecting any one of the two applied voltage levels.
Of course, it is possible to realize those based on three or more voltage levels to be applied to the pair of electrodes and three or more displacement forms or displacement distributions.
It is preferable for the ceramic element constructed as described above that the anti-ferroelectric film after polarization has a region in which its average dielectric constant is increased in an analog manner in accordance with a voltage applied to the electrodes. In this embodiment, when the voltage is applied to the electrodes, the electric field-induced phase transition is caused over a region corresponding to the applied voltage in the anti-ferroelectric film of the operating section. The term xe2x80x9capplied voltagexe2x80x9d refers to an absolute value of the positive or negative voltage.
The operation of the ceramic element according to the present invention will be specifically explained. At first, until the applied voltage arrives at a predetermined voltage in accordance with the gradual increase in applied voltage, the electric field generated in the operating section is weak. Therefore, the electric field-induced phase transition (hereinafter simply referred to as xe2x80x9cphase transitionxe2x80x9d) is not caused in the anti-ferroelectric film.
When the applied voltage exceeds the predetermined voltage, a sufficient electric field intensity is provided to cause the phase transition in a region in which the distance between the electrodes is shortest and in a region which is nearest to the electrodes. The phase transition occurs in these regions, and the mechanical displacement is generated in accordance with the phase transition. The displacement is amplified by the vibrating section, and the operating section is displaced in the first direction (for example, in the direction for the operating section to face the free space).
When the applied voltage is further increased, the region, which has the sufficient electric field intensity to cause the phase transition, is gradually widened. The phase transition also occurs in a region in which the distance between the electrodes is long and in a region which is far from the electrodes. In this stage, the mechanical displacement of the operating section is increased in accordance with the spread of the phase transition area.
That is, in the ceramic element according to the present invention, the displacement in the first direction generated in the operating section is increased in an analog manner in accordance with the increase in applied voltage.
Once the operating section is displaced in the first direction, the displacement is maintained as it is even when the voltage application to the pair of electrodes is stopped (for example, when the electric field is made to be zero). Accordingly, it is unnecessary to continuously apply the voltage to the pair of electrodes even when the displacement generated in the operating section is required to be maintained for a certain period of time. In order to restore the displacement generated in the operating section to the original state, a small reverse bias voltage, specifically a voltage to cause the phase transition from the ferroelectric phase to the anti-ferroelectric phase may be applied to the pair of electrodes.
As described above, in the ceramic element according to the present invention, the mechanical displacement amount is changed in the analog manner depending on the voltage applied to the electrodes. The displacement amount, which is equivalent to that obtained upon the voltage application, can be maintained in the no voltage-loaded state after completion of the application of the voltage to the electrodes.
Accordingly, it is possible to precisely control the magnitude of the displacement amount corresponding to the applied voltage. Moreover, it is possible to obtain a large displacement-generating force which exceeds those obtained in the piezoelectric/electrostrictive film-type element, even when a minute element is used.
In the ceramic element according to the present invention, the displacement amount, which is approximately the same as that obtained upon application of the driving voltage, can be maintained in the no voltage-loaded state and the low voltage-loaded state after completion of the application of the driving voltage. When the ceramic element is applied to a variety of applications (for example, display devices and filters), it is possible to simplify electric wiring for driving the element and effectively reduce the production cost.
In the ceramic element as described above, it is also preferable to combine a plurality of regions in which the average dielectric constant is increased in an analog manner depending on the applied voltage. In this embodiment, a plurality of areas exist depending on the applied voltage, in which the displacement ratio (displacement increase rate) differs. A plurality of displacement forms and/or displacement distributions can be selected depending on the value of the applied voltage. Thus, it is possible to obtain the element which is excellent in, for example, selectivity for the displacement form.
S pecifically, for example, when it is intended to obtain the element excellent in selectivity for the displacement form, it is preferable to provide a region in which a distance between the pair of electrodes Is large and a region in which the distance between the pair of electrodes is small. The region in which the distance between the electrodes is large and the region in which the distance between the electrodes is small are formed by using a pattern of the pair of electrodes. Accordingly, when a constant voltage is applied to the pair of electrodes, a high electric field is always generated in the small-distance region th an in t he large-distance region. Therefore, when the applied voltage is low, only the portion of the anti-ferroelectric film corresponding to the small-distance region is subjected to the phase transition at a certain voltage to cause displacement. Subsequently, when a larger voltage is applied to the pair of electrodes, the large-distance region is subjected to the phase transition at a certain voltage to cause displacement. As a result, the following effect can be obtained. That is, two displacement forms or displacement distributions can be arbitrarily selected by selecting any one of the two applied voltage levels.
Of course, it is possible to realize those based on three or more voltage levels to be applied to the pair of electrodes and three or more displacement forms or displacement distributions.
It is preferable for the ceramic element constructed as described above that the vibrating section and the fixed section are provided on a substrate formed by stacking ceramic green sheets or ceramic green tapes, followed by integrated sintering.
In this embodiment, it is preferable that at least the vibrating section is principally formed of partially stabilized zirconia. Accordingly, it is possible to obtain the vibrating section having high strength and high toughness, making it possible to obtain a long service life of the ceramic element.
It is preferable for the ceramic element constructed as described above that the anti-ferroelectric film principally has the following composition:
Pb0.99Nb0.02{[ZrxSn1-x]1-yTiy}0.98O3
wherein 0.5 less than x less than 0.6, 0.05 less than y less than 0.063, 0.01 less than Nb less than 0.03.
In this embodiment, the large displacement is obtained as compared with the paraelectric phase-anti-ferroelectric phase transition, because the anti-ferroelectric phase-ferroelectric phase transition is utilized. Especially, when the composition described above is used, the anti-ferroelectric phase is stable at room temperature. Therefore, it is possible to easily induce the anti-ferroelectric phase by applying an external electric field, in accordance with which it is possible to cause large strain change.
It is especially preferable that the composition contains Ag in an amount of 1 to 10% by weight as converted into an amount of silver oxide, as a material for the anti-ferroelectric film, in order to obtain more precise and larger displacement, and in order to obtain more stable shape memory characteristics.
In the embodiment described above, Ag may be contained by means of the following methods. That is, Ag may be added in a form of oxide together with other material powders during the process to prepare the anti-ferroelectric film. Alternatively, Ag may be added to a previously prepared anti-ferroelectric material powder, as silver oxide or as an aqueous solution of silver nitrate. Further alternatively, Ag may be mixed in a form of silver oxide powder or in a form of organic metal compound of Ag when a printing paste is prepared.
In a preferred embodiment, the substrate may be formed by stacking a spacer plate provided with a window and a closing plate to be superimposed on one side of the spacer plate so that the window is covered therewith, followed by integrated sintering. In this embodiment, the operating section can be formed in a minute region on the vibrating section, making it possible to realize high density integration for the operating section.
In another preferred embodiment, the substrate may be formed by stacking at least one layer of a base plate to be superimposed on the other side of the spacer plate so that the window is covered therewith, the base plate having one or more through-holes at a position corresponding to the window, followed by integrated sintering together with the spacer plate and the closing plate. In this embodiment, a stacked compact, which is composed of the spacer plate, the closing plate, and the base plate, is integrally sintered to form the vibrating section and the fixed section. However, in general, it is feared that the sintered compact itself may be destroyed due to the increase in pressure at the window, if the integrated sintering is performed while closing both openings of the window. However, in the present invention, one or more through-holes are provided through the base plate. Therefore, the pressure in the window generated during the integrated sintering is released to the outside through the through-hole. Accordingly, the destruction of the stacked compact is avoided, which would be otherwise caused during the integrated sintering. This feature is advantageous to improve the reliability of the vibrating section and the fixed section.
The pair of electrodes are formed on at least a part of the anti-ferroelectric film in accordance with the following embodiments. That is, both of the pair of electrodes may be formed on a first principal surface of the anti-ferroelectric film. Alternatively, one of the pair of electrodes may be formed on a first principal surface of the anti-ferroelectric film, and the other electrode may be formed on a second principal surface of the anti-ferroelectric film.
Especially, when the pair of electrodes are formed on the first principal surface of the anti-ferroelectric film, it is preferable to satisfy p/txe2x89xa62.5 provided that an average film thickness of the anti-ferroelectric film is t, and a pitch between the electrodes is p. It is preferable that the vibrating section principally comprises partially stabilized zirconia containing not less than 0.5 mole % of alumina. In this embodiment, the anti-ferroelectric film is directly formed on the vibrating section. Therefore, the anti-ferroelectric film is tightly joined to the vibrating section. Thus, it is possible to obtain the ceramic element having a large displacement amount.
When one of the electrodes is formed on the first principal surface of the anti-ferroelectric film, and the other electrode is formed on the second principal surface of the anti-ferroelectric film, it is preferable to satisfy A/Bxe2x89xa72 or A/Bxe2x89xa60.5 provided that an area of the one electrode is A, and an area of the other electrode is B. Alternatively, it is preferable that a region interposed between the electrodes has a film thickness distribution which involves dispersion of not less than 20%.
Especially, when the electrodes have the form as described above, it is preferable that the vibrating section is principally composed of partially stabilized zirconia containing not less than 0.5 mole % of titanium oxide. In this embodiment, the anti-ferroelectric film is tightly joined to the vibrating section by the aid of the other electrode. Therefore, the reliability is improved. Further, the anti-ferroelectric film is not secured to the vibrating section in the region in which the electrode does not exist on the surface to which the anti-ferroelectric film and the vibrating section are opposed. Accordingly, it is possible to obtain the ceramic element having a large displacement amount without restricting the vibrating displacement of the operating section.
When the pair of electrodes are formed on the first principal surface of the anti-ferroelectric film, an intermediate layer may be provided between the vibrating section and the anti-ferroelectric film. In this embodiment, the intermediate layer is preferably a metal of Pt or Pd or an alloy of the both metals. It is appropriate that a thickness of the intermediate layer is not less than 1 xcexcm and not more than 10 xcexcm. It is preferable that the thickness of the intermediate layer is not less than 2 xcexcm and not more than 6 xcexcm.
It is preferable for the ceramic element constructed as described above that a thickness of the vibrating section is thinner than a thickness of the anti-ferroelectric film. In this embodiment, it is appropriate that a thickness tb of the substrate satisfies tbxe2x89xa6350 xcexcm when Ln less than tvxc3x9715 is satisfied provided that a boundary portion between an upper surface of the fixed section and an upper surface of the vibrating section concerning a shortest dimension passing through a center of the vibrating section is defined as a boundary point, a distance from the boundary point to an end of a region in which the anti-ferroelectric film is formed is Ln, and a thickness of the vibrating section is tv. Preferably, tbxe2x89xa6250 xcexcm is satisfied. More preferably, tbxe2x89xa6130 xcexcm is satisfied. Most preferably, tbxe2x89xa670 xcexcm is satisfied.
When the distance Ln from the boundary point to the end of the region in which the anti-ferroelectric film is formed satisfies Lnxe2x89xa7tvxc3x9715, the thickness tv of the vibrating section is preferably 1 to 50 xcexcm, and more preferably 3 to 20 xcexcm. On the other hand, an average thickness of the anti-ferroelectric film 22 is preferably 1 to 100 xcexcm, more preferably 3 to 50 xcexcm, and most preferably 5 to 40 xcexcm.
It is desirable that the anti-ferroelectric film formed on the substrate is obtained by performing a sintering treatment while applying a load. In this embodiment, it is preferable that the load is not less than 0.4 kg/cm2. Further, it is preferable that a depth of a space disposed just under the vibrating section is not more than 10 xcexcm.
According to another aspect of the present invention, there is provided a method for producing a ceramic element comprising an operating section having an anti-ferroelectric film and at least a pair of electrodes formed on the anti-ferroelectric film, a vibrating section for supporting the operating section, and a fixed section for supporting the vibrating section in a vibrating manner; the method comprising the steps of stacking ceramic green sheets or ceramic green tapes followed by integrated sintering to prepare a substrate having the vibrating section and the fixed section; forming the anti-ferroelectric film on the vibrating section of the substrate; and sintering the anti-ferroelectric film.
In this aspect, it is preferable that the anti-ferroelectric film is subjected to a sintering treatment while applying a load thereto. More desirably, the load is not less than 0.4 kg/cm2.
In the production method described above, it is preferable that an anti-ferroelectric ceramic material is prepared to have a powder composition which is deviated from an optimum composition when a powder of the anti-ferroelectric ceramic material is prepared to produce the anti-ferroelectric film, while speculating variation in composition due to mutual diffusion with respect to the vibrating section during the sintering for the anti-ferroelectric film. In this embodiment, the material is prepared such that ZrO2 is weighed in an amount smaller than its prescribed amount, and TiO2 is weighed in an amount larger than its prescribed amount. Specifically, it is preferable that the amount of ZrO2 is 95 to 98% provided that the prescribed amount is 100%, and/or the amount of TiO2 is 102 to 104% provided that the prescribed amount is 100%.
It is preferable that when a powder of an anti-ferroelectric ceramic material is prepared to produce the anti-ferroelectric film, the powder is previously prepared in a composition in which lead oxide is contained in an amount smaller than its prescribed blending amount, and then an amount of shortage of lead component is compensated and mixed afterward in a form of lead oxide.
In this embodiment, an amount of post-compensation for the lead component is preferably not less than 3% and not more than 20% of the prescribed blending amount, and more preferably not less than 5% and not more than 15% thereof.
It is preferable that when a powder of an anti-ferroelectric ceramic material is prepared to produce the anti-ferroelectric film, a specific surface area of tin oxide to be used as a raw material is not less than 8 m2/g and not more than 20 m2/g.
In the production method described above, it is preferable that the substrate is formed by stacking a second layer provided with a window, a third layer to be superimposed on one side of the second layer so that the window is covered therewith, and a first layer to be superimposed on the other side of the second layer so that the window is covered therewith, the first layer having one or more through-holes at a position corresponding to the window, followed by integrated sintering to produce the substrate made of ceramic.
In another embodiment of the production method, it is preferable that a paste composed of a ceramic material is formed as a pattern on an upper surface of a first layer having one or more through-holes, a second layer having a window is formed at a portion corresponding to the through-hole, and then a third layer is stacked to close the window, followed by integrated sintering to produce the substrate made of ceramic.
When the substrate is produced, it is preferable that a thickness of the second layer is 1 to 15 xcexcm.
According to still another aspect of the present invention, there is provided a display device comprising an optical waveguide plate for introducing light thereinto, and a driving unit provided opposingly to one plate surface of the optical waveguide plate and including a number of actuator elements arranged corresponding to a large number of picture elements, for displaying, on the optical waveguide plate, a picture image corresponding to an image signal by controlling leakage light at a predetermined portion of the optical waveguide plate by controlling displacement action of each of the actuator elements in a direction to make contact or separation with respect to the optical waveguide plate in accordance with an attribute of the image signal to be inputted; wherein the actuator element comprises a main actuator element having an anti-ferroelectric film and at least a pair of electrodes formed on the anti-ferroelectric film, a vibrating section for supporting the main actuator element, and a fixed section for vibratingly supporting the vibrating section, the display device further comprising a displacement-transmitting section for transmitting, to the optical waveguide plate, the displacement action of the actuator element generated by applying a voltage to the pair of electrodes.
Accordingly, at first, all of the light, which is introduced, for example, from the end of the optical waveguide plate, is totally reflected at the inside of the optical waveguide plate without being transmitted through the front and back surfaces of the optical waveguide plate, by regulating the magnitude of the refractive index of the optical waveguide plate. In this state, for example, when the displacement-transmitting section contacts with the back surface of the optical waveguide plate at a distance of not more than the wavelength of the light, then the light, which has been totally reflected, is transmitted to the surface of the displacement-transmitting section contacting with the back surface of the optical waveguide plate. The light, which has once reached the surface of the displacement-transmitting section, is reflected by the surface of the displacement-transmitting section, and the light behaves as scattered light. A part of the scattered light is reflected again at the inside of the optical waveguide plate. However, almost all of the scattered light is not reflected by the optical waveguide plate, and the light is transmitted through the front surface of the optical waveguide plate.
As described above, it is possible to control the presence or absence of light emission (leakage light) at the front surface of the optical waveguide plate, depending on the presence or absence of the contact of the displacement-transmitting section disposed at the back of the optical waveguide plate. In this case, one unit for allowing the displacement-transmitting plate to make the displacement action in the direction to give contact or separation with respect to the optical waveguide plate may be regarded as one picture element. Thus, a picture image (for example, characters and graphics) corresponding to an image signal can be displayed on the front surface of the optical waveguide plate in the same manner as the cathode ray tube and the liquid crystal display device, by arranging a large number of such picture elements in a matrix form, and controlling the displacement action of each of the picture elements in accordance with an attribute of the inputted image signal.
According to still another aspect of the present invention, there is provided a relay device comprising an opposing terminal section, and a driving unit provided opposingly to one side of the opposing terminal section and including a number of actuator elements arranged corresponding to a large number of switching elements, for switching and controlling ON/OFF operation of the switching element by controlling displacement action of each of the actuator elements in a direction to make contact or separation with respect to the opposing terminal in accordance with an attribute of a driving signal to be inputted; wherein the actuator element comprises a main actuator element having an anti-ferroelectric film and at least a pair of electrodes formed on the anti-ferroelectric film, a vibrating section for supporting the main actuator element, and a fixed section for vibratingly supporting the vibrating section, the relay device further comprising a signal terminal section for transmitting, to the opposing terminal section, the displacement action of the actuator element generated by applying a voltage to the pair of electrodes.
Accordingly, the signal terminal section of one of the large number of switching elements contacts with the opposing terminal section, the signal terminal section is electrically connected to the opposing terminal section. A signal is transmitted between the signal terminal section and the opposing terminal section. Thus, for example, the ON operation is performed.
As described above, it is possible to control the ON/OFF operation of the large number of switching elements depending on the presence or absence of the contact of the signal terminal section disposed at the back of the opposing terminal section. In this case, one unit for allowing the signal terminal section to make the displacement action in the direction to give contact or separation with respect to the opposing terminal section may be regarded as one switching element. Thus, a large number of combinations of switching forms can be provided, for example, by arranging a large number of such switching elements in a matrix form, and controlling the displacement action of each of the switching elements in accordance with an attribute of the inputted switching signal.
The relay device according to the present invention includes the main actuator element for making selective displacement of the signal terminal section, the main actuator element comprising the anti-ferroelectric film, and at least one pair of electrodes formed on the anti-ferroelectric film. In this arrangement, when a predetermined voltage is applied to the pair of electrodes, an electric field is generated in the main actuator element depending on the applied voltage. The generated electric field allows the anti-ferroelectric film to make displacement, for example, in the first direction. The displacement of the anti-ferroelectric film in the first direction causes the signal terminal section to displace toward the opposing terminal section. Thus, the ON operation of the switching element is induced as described above.
Especially, as described above, once the anti-ferroelectric film undergoes the displacement, the displacement is maintained even when the no voltage-loaded state is given. Therefore, after the voltage is :applied to the necessary switching element for performing the switching operation to displace the main actuator element of the necessary switching element, the displacement is maintained to continue the ON operation of the necessary switching element over a period until the displacement is counteracted, even when the voltage application to the pair of electrodes concerning the necessary switching element is stopped. Accordingly, electric power consumption is greatly reduced, and it is possible to realize reduction of running cost.
When the switching control is performed by specifying rows and columns, it is enough to apply the voltage to only a switching element column corresponding to a concerning row. It is unnecessary to consider voltage application to the other switching element columns. Therefore, when electric wiring is arranged for driving the element, it is unnecessary to arrange wiring for each of elements one by one in an individual manner. Thus, it is possible to simplify the electric wiring. This results in the reduction of load exerted on the system for supplying the driving voltage. Accordingly, it is possible to simplify the mechanical structure and the circuit arrangement and reduce the production cost.
According to still another aspect of the present invention, there is provided a capacitor comprising a vibrating section for supporting a capacitor unit, and a fixed section for vibratingly supporting the vibrating section, wherein the capacitor unit comprises an anti-ferroelectric film formed on the vibrating section, a pair of control electrodes formed on an upper surface of the anti-ferroelectric film, and both terminal electrodes of the capacitor formed on the upper surface and a lower surface of the anti-ferroelectric film respectively.
Accordingly, it is possible to easily construct a capacitance-variable capacitor in which the capacitance appearing between the both terminal electrodes is changed in an analog manner in accordance with the increase in voltage applied to the pair of control electrodes. Further, the capacitor can be formed as one of the thin film-type. Therefore, it is possible to facilitate miniaturization of, for example, parametric amplifiers incorporated with the variable capacitor, automatic frequency control circuits (AFC), and various types of communication instruments.